A resonator fiber optic gyroscope (RFOG) has the potential to be a rotation rate sensing device with high accuracy in a compact size. To avoid back-reflected light from interfering with signal light, multiple frequency light sources with different carrier frequencies have been proposed to measure the resonance frequency difference between the clockwise (CW) and counter-clockwise (CCW) direction. This uses two or more light beams locked to neighboring resonances to calculate the rotation rate.